Influences of sleep and the circadian rhythm on iron-status indices

ObjectivesThe aim was to study the influence of sampling time, food intake and sleep on tests used to screen for and monitor conditions of iron deficiency and overload.Design and methodsThe 24 h variations of iron, transferrin, transferrin saturation (TS) and ferritin were studied in seven healthy individuals during standardised food intake, and during night or day sleep.ResultsIron and TS showed clear diurnal variations, with peaks at 12.6 h and 12.8 h respectively, during night sleep, and at 19.7 h and 19.3 h, respectively, during day sleep. Ferritin did not demonstrate any circadian variation. Transferrin and ferritin were unaffected by sleep-condition. Meals did not have any effect except a slight decline of transferrin.ConclusionsTime of day and sleeping patterns had great influence on iron and TS, whereas no or only minor effects are seen on the concentration of ferritin and transferrin. Meals have limited effects.